Dirksen attended the University of Minnesota, left before graduating to serve in World War I, and, after his discharge, returned to Pekin, where he pursued a number of business interests. In 1926, with his election to the office of city finance commissioner in Pekin, Dirksen began what was to become a lifelong career in public service. Defeated in 1930 in his bid for a congressional seat, he ran again in 1932 and won. A conservative Republican, Dirksen voted against most New Deal measures—except Social Security. He also opposed Franklin D. Roosevelt’s foreign policy, adhering to an isolationist stance. In a foreshadowing of his later moderation and flexibility, however, Dirksen switched to bipartisan support of presidential foreign policy with U.S. entry into World War II.

A severe eye ailment forced Dirksen to resign his House seat in 1948. He returned to Pekin to practice law, having gained admittance to the bar by examination while serving in Congress. By 1950 his health was fully restored, and he ran successfully for a seat in the Senate. Throughout the 1950s, Dirksen belonged to the so-called old guard conservative wing of the Republican Party. He backed Sen. Robert A. Taft for the 1952 presidential nomination, and he supported the anticommunist crusade of Joseph R. McCarthy until the Wisconsin senator was discredited in the middle of the decade.

In his constituency, in the Senate, and through the medium of television, Dirksen became something of a folk hero for his rich bass voice and imposing oratorical style, attributes for which his critics dubbed him “the wizard of ooze.” He won his last election in 1968 and served in the Senate until his death the following year.